Blackbody temperatures of CaO shoccked to prssures from 140 to 182 GPa have been measure in the 3750 to 6000 K range using the Lawrence Livermore National Laboratory light gas gun. These shock temperatures, along with Hugoniot data for single crystal and porouss CaO and isothermal data, are used to construct equations of state for the high pressure (B2) phase of CaO. The zero-pressuure density of the B2 phase is between 3.8 and 4.0 Mg/m3 and th B1-B2 transition energy is 2.1 to 2.3 MJ/kg. The density and bulk modulus at pressures from 70 to 135 GPa are similar to seismically determined values for the lower mantle of the earth. Thus the lower mantle could have a substantial inventory of Ca-bearing minerals, and mixed oxide models, for the composition of the lower mantle will be insensitive to the quantity of CaO assumed.